Stage 4 Glacier Extents in the Middle Latitudes of the Southern Hemisphere
Abstract
Marine Isotope Stage (MIS) 4 has traditionally been considered less extreme than MIS 2, an interpretation based in part on globally integrated marine records. This assumption is put into question by recently developed local and regional-scale paleo records. It has gone untested until recently in part because it is beyond the radiocarbon limit and applications of surface exposure dating of moraine ridgetops has been limited mostly to sequences up to the beginning of MIS 2. It is difficult to create well-constrained records with moraine ridgetop boulder dating beyond MIS 2 in most places because denudation and erosion of moraine and boulder surfaces reduce the concentration of surface cosmogenic nuclides in an unsystematic way. Here we present two precisely dated MIS 4 glacial moraine records from well-preserved moraine sequences at the Strait of Magellan, Chile (53°S) and a published MIS 4 advance of the Pukaki Glacier, New Zealand (44°S; Schaefer et al., 2015). The preservation of MIS 4 moraines in these two valleys means that the glaciers extended farther down-valley during MIS 4 than MIS 2, which suggests it may have been colder and wetter during this time. We apply the University of Maine Ice Sheet Model to the Strait of Magellan lobe to calculate the possible combinations of temperature and precipitation departures necessary to achieve the dated and mapped MIS 4 extent. Geomorphic mapping of the Strait of Magellan lobe shows that during MIS 4, the glacier lobe extended all the way out to the Atlantic, beyond Primera Angostura, meaning that the Strait of Magellan lobe would have coalesced with the Otway lobe and indicates that at least some glacial deposits in the area are younger than previously thought. Lastly, we compare these glacial records with published Southern Hemisphere ice core dust and marine records to place them in a larger Southern Hemisphere context.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP31F1722K
- Keywords:
-
- 4914 Continental climate records;
- PALEOCEANOGRAPHYDE: 4926 Glacial;
- PALEOCEANOGRAPHYDE: 4946 Milankovitch theory;
- PALEOCEANOGRAPHYDE: 4954 Sea surface temperature;
- PALEOCEANOGRAPHY